Curing of alkali terminated polymers



3,048,568 CURING fil ALKALI TERMINATED PGLYMERS James W. ClearBartlesville, Qkla, assignor to Phillips Petroleum (Zornpany, acorporation of Delaware No Drawing, Filed July 13, 1959, Ser. No.826,392 21) Claims. (Cl. 260-79) This invention relates to self-curingpolymers prepared by reacting terminally reactive polymers with a cyclicdisulfide. In one aspect the invention relates to solid polymer preparedby heat-curing polymers obtained by reacting polymers containingterminal alkali metal atoms with a cyclic disulfide. In still anotheraspect of the invention curing is carried out in the presence of aconventional curing system.

As used herein the term terminally reactive polymer designates polymerwhich contains a reactive group at one or both ends of the polymerchain.

It is an object of this invention to provide new and useful polymericmaterials and process for their prepa ration.

Another object of this invention is to provide selfcuring polymers frompolymers containing terminal alkali metal atoms and process for theirpreparation.

Still another object of this invention is to provide cured polymers frompolymers obtained by reacting polymers containing terminal alkali metalatoms with a cyclic disulfide.

These and other objects of the invention will become more readilyapparent from the following detailed description and discussion.

The foregoing objects are realized broadly by reacting a polymercontaining terminal alkali metal atoms with a cyclic disulfide andreplacing alkali metals in the polymer product with hydrogens to obtaina polymer containing terminal mercapto groups.

In one aspect of the invention the polymer product is subjected to heatwhereby molecules of said polymer react with each other to form a curedpolymer.

In another aspect of the invention curing of the polymer product iscarried out in the presence of a conventional curing system.

The monomers which can be employed in the preparation of polymerscontaining terminal alkali metal atoms include a Wide variety ofmaterials. The preferred monomers are the conjugated dienes containingfrom 4 to 12 carbon atoms and preferably 4 to 8 carbon atoms, such as1,3-butadiene, isoprene, piperylene, methylpen-tadiene, phenylbutadiene,3,4-dimethyl-1,3-hexadiene, 4,5- diethyl-l,3-octadiene, etc. Inaddition, conjugated dienes containing reactive substituents along thechain can also be employed, such as for example, halogenated dienes,such as chloroprene, fluoroprene, etc. Of the conjugated dienes thepreferred material is butadiene, with isoprene and piperylene also beingespecially suitable. In addition to the conjugated dienes other monomerswhich can be employed are aryl-substituted olefins, such as styrene,various alkyl styrenes, paramethoxystyrene, vinylnaphthalene,vinyltoluene, and the like; heterocyclic nitrogencontaining monomers,such as pyridine and quinoline derivatives containing at least 1 vinylor 'alphamethyl-vinyl group, such as Z-vinylpyridine, 3-vinylpyridine,4-vinylpyridine, 3-ethyl-5-vinylpyridine, Z-methyl-S-vinylpyridine,3,5-diethyl-4-vinylpyridine, etc.; similar monoand (ii-substitutedalkenyl pyridines and like quinolines; acrylic acid esters, such asmethyl acrylate, ethyl acrylate; alkacrylic acid esters, such as methylmethacrylate, ethyl methacrylate, propyl methacrylate, ethylethacrylate, butyl methacrylate; methyl vinyl ether, vinyl chloride,vinylidene chloride, vinylfuran, vinylcarbazole, vinylacetylene, etc.

3,04%,568 Patented Aug. '7, 1962 ire The above compounds in addition tobeing polymerizaable alone are also copolymerizable with each other andmay be copolymerized to form terminally reactive polymers. In addition,copolymers can be prepared using minor amounts of copolymerizablemonomers containing more than one vinylidene group such as2,4-divinylpyridine, divinylbenzene, 2,3-divinylpyridine,3,5-divinylpyridine, 2,4-divinyl-6-methylpyridine,2,3-divinyl-5-ethylpyridine, and the like.

The terminally reactive polymers in addition to including homopolymersof polymerizable vinylidine compounds and ccpolymers of conjugateddienes with vinylidine compounds also include block copolymers, whichare formed by polymerizing a monomer onto the end of a polymer, themonomer being introduced in such a manner that substantially all of theco-reacting molecules enter the polymer chain at this point. In general,the block copolymers can include combinations of homopolymers andcopolymers of the materials hereinbefore set forth. A detaileddescription of block copolymers containing terminal reactive groups andtheir method of preparation is set forth in the copending application ofR. P. Zelinski, Serial No. 796,277, filed March 2, 1959.

The terminally reactive polymers are prepared by contacting the monomeror monomers which it is desired to polymerize with an organo alkalimetal compound. The organo alkali metal compounds preferably containfrom 1 to 4- alkali metal atoms, and those containing 2 alkali metalatoms are more often employed. As will be expalined hereinafter, lithiumis the preferred alkali metal.

The organo alkali metal compounds can be prepared in several ways, forexample, by replacing halogens in an organic halide with alkali metals,by direct addition of alkali metals to a double bond, or by reacting anorganic halide with a suitable alkali metal compound.

The organo alkali metal compound initiates the polymerization reaction,the organo radical being incorporated in the polymer chain and thealkali metal being attached terminally at at least one end of thepolymer chain. When employing polyalkali metal compounds an alkali metalis attached terminally at each end of the polymer chain. The polymers ingeneral will be linear polymers having two ends; however, polymerscontaining more than two ends can be prepared Within the scope of theinvention. These polymers can be represented by the general formula PTwhere P comprises the polymer as previously described and T is an alkalimetal, x being an integer of l to 4. The general reaction can beillustrated graphically as follows:

Organoalkali metal compound Butadiene or combinations thereof.

A specific example is:

compounds which give very high conversions to the terminally reactivepolymer. With organo compounds of the other alkali metals, the amount ofmonoterminally reactive polymer, that is, polymer having alkali metal atonly one end of the chain is substantially higher. The alkali metals, ofcourse include sodium, potassium, lithium, rubidium, and cesium. Theorganic radical of the organo alkali metal compound can be an aliphatic,cycloaliphatic or aromatic radical. For example, mono, diand polyalkalimetal substituted hydrocarbons can be employed including methyllithium,n-butyllithium, n-decyllithium, phenyllithium, naphthyllithium,p-tolyllithium, cyclohexyllithium, 4-butylphenylsodium,4-cyclohexylbutylpotassium, isopropylrubidium, 4-pheny1butylcesium,1,4-dilithiobutane, 1,5-dipotassiopentane, 1,4-disodio-2-methylbutane,1,6-dilithiohexane, 1,10-dilithiodecane, 1,15-dipotassiopentadecane,1,20-dilithieicosane, 1,4-disodio-2- butene,l,4-dilithio-2-methyl-2-butene, 1,4-dilithio-2-butene,1,4-dipotassio-2-butene, dilithionaphthalene, disodionaphthalene,4,4-dilithiobiphenyl, disodiophenanthrene, dilithioanthracene,1,2-dilithio-1,ldiphenylethane, 1 ,2-disodio-1,2,3-triphenylpropane,1,Z-dilithio-1,2-diphenylethane, l,Z-dipotassiotriphenylethane,1,2-dilithiotetraphenylethane, 1,2-dilithio-1-phenyl-l-naphthylethane,1,2-dilithio-1,2-dinaphthylethane, 1,2-disodio-1, l-diphenyl-2-naphthylethane, l,2-dilithiotrinaphthylethane, 1,4-dilithiocyclohexane,2,4-disodioethylcyclohexane, 3,5-dipotassion-butylcyclohexane,1,3,S-trilithiocyclohexane, 1-lithio-4- (2-lithiomethylphenyl)butane,1,2 dipotassio 3 phenylpropane, 1,2-di(lithiobutyl)benzene,1,3-dilithio-4-ethylbenzene, 1,4-dirubidiobutane, 1,8-dicesiooctane,1,5,12- trilithiododecane, 1,4,7 tnisodioheptane, 1,4 di(1,2, di-Iithio-Z-phenylethyl)benzene, l,2,7,S-tetrasodionnaphthalene,1,4,7,lO-tetrapotassiodecane, 1,5-dilithio-3-pentyne,1,8-disodio-5-octyne, 1,7-dipotassio-4-heptyne, 1,10-dicesio-4-decyne,1,1l-dirubidio-S-hendecyne, l,2-disodio- 1,2-diphenylethane,dilithiophenanthrene, l,2-dilithiotriphenylethane, 1,2 disodio 1,2diphenylethane, dilithiomethane, 1,4 dilithio 1,l,4,4 tetraphenylbutane,1,4- dilithio-I,4-diphenyl-1,4-dinaphthylbutane, and the like.

' While the organo alkali metal initiators in general can be employed,certain specific initiators give better results than others and arepreferred in carrying out the preparation of the terminally reactivepolymers. For example, of the condensed ring aromatic compounds thelithium-naphthalene adduct is preferred, but the adducts of lithium withanthracene and biphenyl can be employed with good results. Of thecompounds of alkali metals with polyaryl-substituted ethylenes, thepreferred material is 1,2-dilithio-1,Z-diphenylethane (lithium-stilbeneadduct). Ordinarily the dilithio compounds are preferred as being moreeliective in promoting the formation of the terminally reactivepolymers. The organo dialkali metal compounds which have been set forthas being preferred, are those which when prepared contain a minimum ofthe monoalkali metal compound.

The amount of initiator which can be used will vary depending on thepolymer prepared, and particularly the molecular weight desired. Usuallythe terminally reactive polymers are liquids, having molecular weightsin the range of 1000 to about 20,000. However, depending on the monomersemployed in the preparation of the polymers and the "amount of initiatorused, semi-solid and solid terminally reactive polymers can be preparedhaving molecular weights up to 150,000 and higher. Usually the initiatoris used in amounts between about 0.25 and about 100 millimoles per 100grams of monomer.

.Formation of the terminally reactive polymers is generally carried outin the range of between 100 and '+150 C., preferably between -75 and +75C. The particular temperatures employed will depend on both the monomersand the initiators used in preparing the polymers. For example, it hasbeen found that the oraromatics containing from 4 to 10 carbon atoms permolecule. As stated previously, the organodilithium compounds arepreferred as initiators in the polymerization reaction since a verylarge percentage of the polymer molecules formed contain two terminalreactive groups, and also the polymerization can be carried out atnormal room temperatures. This is not to say, however, that other organoalkali metal initiators cannot be employed; however, usually morespecialized operation or treatment is required with these materials,including low reaction temperatures. Since it is desirable to obtain amaximum yield of terminally reactive polwner, it is within the scope ofthe invention to use separation procedures, particularly with alkalimetal initiators other than lithium compounds, to separate terminallyreactive polymer from the polymer product.

The terminally reactive polymers prepared as hereinbefore describedcontain an alkali metal atom on at least one end of the polymer chainand the organo radical of the initiator is present in the polymer chain.These polymers are rendered self-curing by reaction with a cyclicdisulfide selected from the group consisting of wherein R is selectedfrom the group consisting of hydrogen and alkyl radicals containing from1 to 30 carbon atoms, and Y is a divalent organic radical containingfrom 1 to 12 chain members (not necessarily carbon) selected from thegroup consisting of alkylene radicals, alkenylene radicals and radicalscontaining groups se lected from the group consisting of I O, N, and Ssaid groups being linked between carbon atoms, where each R is an alkylradical containing 1 to 3 carbon atoms.

The reaction, in which P is a polymer, in its simplest form is believedto occur as follows Specific cyclic disulfides which can be used incarrying out the invention include 1,2-dithiacycloocta-4,6-diene,1,Z-dithia-S,8-dioxacyclodecane, 2,2'-biphenylene disulfide,4,4'-dimethyl-2,2-biphenylene disulfide, 3,5-diethyl-2,2-biphenylenedisulfide, 4,4-diisopropyl-2,2-biphenylene disulfide,1,Z-dithiacyclohexadecaue, 3,4,5,6-tetramethyl-LZ-dithiacyclohexadecane,3 ,5 ,7-tri-n-propyl-1,2-dithiacycloheptane, 1,2-dithiacyclohexadeca-5,7,l 1,13-tetraene,

3 ,l 6-dimethyl-1 ,Z-dithiacyclohexadeca-S ,8, 1 1,14-tetraene,1,2-dithiacyclodeca-4,6,8-triene,

3 ,5 ,7-triisopropyl- 1 ,Z-dithiacyclohexane, 3-methyl-6-ethyl-l,Z-dithiacyclohexane, 3,6-diisopropyl-1,2-dithiacyclohex-4ene,

1 ,2-dithiacyclopent-3 -e11e,

3 -methyl-8-e thyl-l ,2-dithiacyclooct-5 -ene,

1 ,Z-dithi a-6-oxacyclononane,

3 ,5 -dimethyl- 1 ,Z-dithiacyclop cut-3 -ene,

3 ,1 0-dimethyl-1,2-dithia-5 ,8-dioxacyclo decane,S-etlhyl-1,Z-dtithitt-S-azacycloheptane,3,8-diethyl-4,7-dimethyl-1,2-ditl1ia-4,7-diazacyclodecane, 4-methyl-l,2-dithia-4-azacyclopentane,5,7-dimethyl-1,Z-dithia-S,7-diazacyclononane,3-methyl-7-ethyl-l,2,S-trithiacycloheptane, and1,2,5,9-tetrathiacycloundecane.

While any of the above and other compounds can be employed the preferredcyclic disulfides are 1,2-dithiacyclopentane, 1,2-dithiacyclohexane and1,2-dithiacycloheptane. Cyclic disulfides can be prepared according tothe method of Tobolsky et al., US. Patent 2,728,750. Barber and Smiles,J. Chem. Soc. 1928, 1141-1149, describe a method of preparing compoundssuch as 2,2- biphenylene disulfide.

In carrying out the preparation of the self-curing polymer the cyclicdisulfide is added to an unquenched solution of terminally reactivepolymer. By unquenched polymer is meant polymer which has not beentreated with any type of reagent to inactivate the initiator. Additionof cyclic disulfide to the polymer solution can be effected by a numberof methods. For example, the cyclic disulfide can be added to theunquenched polymer solution in the dry state or as a solution, or in thealternative, polymer solution can be added to a solution of the cyclicdisulfide. Suitable solvents for the disulfides include materials whichare employed as diluents in the preparation of the polymers containingterminal alkali metal atoms. Whichever method is employed, it isdesirable that the operation be carried out in such a manner as tomaintain the system as fluid as possible. When a polymer chain has onlyone active end group, the reaction system ordinarily remains fiuid whenthe cyclic disulfide is added. In such instances the disulfide can beemployed without first dissolving it in the solvent and can be added allat once. In the situations where it is more difficult to keep the systemfluid, i.e., when there are a plurality of active end groups present,the cyclic disulfide is preferably employed as a solution. The disulfidecan be added incrementally to the polymer solution with agitation aftereach addition or slow continuous addition with simultaneous agitationcan be employed. Generally, the same type of addition procedure is usedwhen a polymer solution is added to a solution of the disulfide.

6 After all of the disulfide reagent has been added to the unquenchedpolymer solution agitation is usually continued for aperiod which canvary from 1 minute to as long as 24 hours or longer.

Reaction of the cyclic disulfide with the terminally reactive polymercan be carried out over a wide range of temperature. In general asuitable reaction temperature is l00 to C., and preferably from about 30to +50 C. The particular reaction temperature employed is determined bythe nature of the polymer being treated and by the disulfide treatingagent which is used. The amount of cyclic disulfide which is provided inthe reaction system is sufiicient to provide a self-curing polymercomposition. Usually the cyclic disulfide is added to the unquenchedpolymer solution in an amount to provide at least 50 percent of themaximum titratable mercaptan that can be obtained, i.e., at least 0.5mole of cyclic disulfide per gram atom of alkali metal present in thepolymer. An excess of cyclic disulfide can be used but preferably notmore than about three moles are added per gram atom of alkali metal. Theproduct which is ob tained from the treatment of the terminally reactedpolymer with the cyclic disulfide is hydrolyzed or reacted with areagent which is capable of replacing the alkali metal atoms withhydrogen atoms. Suitable reagents which can be used include dilutemineral acids, glacial acetic acid, or other organic acids, a mixture ofacid and alcohol, and the like. This reaction, in which P is polymer,takes place generally as follows Although the alkali metal mercaptidecan be titrated to determine the number of active polymer end groups, itis apparent from the foregoing reaction that the hydrolysis stepconverts alkali metal mercaptide groups in the polymer to mercaptogroups, which can also be titrated to determine the number of active endgroups present in the polymer composition. A convenient method fordetermining titratable mercaptan is the amperometric method using silvernitrate. Recovery of the polymer composition containing mercapto endgroups can be effected by washing the polymer solution with water toremove any water soluble ingredients followed by removal of solvent, forexample, by evaporation under reduced pressure or by precipitation ofthe polymer from the solvent with an alcohol such as methanol, ethanol,isopropanel and the like. The product can then be dried under vacuum inan inert atmosphere such as nitrogen or carbon dioxide. Beforeseparation of the polymer product from the hydrocarbon solvent, it maybe desirable to add an antioxidant, for example, a conventional rubberantioxidant such as phenyl-beta-naphthylamine,di-tert-butylhydroquinone, 2,2-methylenebis(4-methyl-fi-terPbu-tylphenol) or the like.

The polymer products of this invention are self-cu ring, i.e., they canbe cured by heating alone, without the use of auxiliary curatives. Thecuring occurs by reaction of the mercapto groups with double bonds in thsame or different polymer chains and the degree of cure which results isdetermined by the amount of mercapto groups in the polymer.

The curing reaction can be illustrated as follows heat where n can varyfrom 0 to x-1.

Curing is usually carried out by heating the polymer to temperatures inthe range of between about 100 and about 500 F. and preferably betweenabout 200 and 400 F. The time required for curing depends on the temperature, the particular polymer being cured and the degree of curingdesired. Usually curing is carried out over a period ranging from as lowas tWo minutes to as high as 24 hours or higher.

In combination wtih heat curing it is within the scope of the inventionto provide conventional auxiliary curing agents, such as sulfur, oxygen,organic peroxides and hydroperoxides, azo bisbutylronitrile and diazothioethers. Materials which are free radical generators are ordinarilyregarded as being useful as curatives in these systems. A particularlyeffective curing agent is dicurnyl peroxide. Other materials Well knownas rubber curing agents include Santocure(N-cyclohexyl-Zbenzothiazylsulfenamide), Altax (benzothiazyl disulfide),Methyl Tuads (tetramethyl thiuram disulfide), and N,N-dimethyl-S-tert-bu-tylsulfenyl dithiocarbarnate. The auxiliary curing agents canbe used when a tighter or greater degree of cure is desired than can beobtained by heat alone.

The self-curing polymers of this invention can be compounded withvarious reinforcing agents and fillers which are ordinarily employed inthe rubber industry, such as carbon black and mineral fillers. Usuallythe polymers prior to curing are liquid and semi-solid, and areconverted by the curing operation to rubbery products. However, it isalso within the scope of the invention to cure polymers which areoriginally rubbery or solid. The wide variety of products obtained whenoperating in accordance with the invention provide materials Which aresuitable for use as adhesives, potting compounds, binders in castalblecompositions and tread stocks.

The reaction between a cyclic disulfide and polymer containing terminalalkali metal atoms is quantitative. The method of this inventiontherefore has an additional application in that it can be utilized fordetermining the alkali metal content of polymer by first treating thepolymer containing terminal metal atoms with the cyclic disulfide andthen measuring the mercaptan content. The amount of mercaptan is ameasure of alkali metal atoms originally present in the polymer.Reaction with polymers containing terminal alkali metal atoms andacyclic disulfides is also quantitative and can be utilized for thisanalytical method.

The following examples are presented in illustration of the invention.

Example I Butadiene was polymerized in accordance with the followingrecipe:

Butadiene parts by weight 100 Cyclohexane do 650 l-lithiobutane 1 partsby weight 2.13 (33.3 millimoles) Temperature, C 50 Time, hours 1.25Conversion, percent 1.00

1 Employed as a solution in n-pentane.

shaken at intervals and after 70 minutes a sample was removed andtitrated amperometrically with silver nitrate. The result indicated thatmercaptan was formed in quantitative yield.

The method described by Barltrop et al., J. Am. Chem. Soc. 76, 4348(1954), can be used to prepare 1,2-dithiane.

The reaction mixture was treated with 8.3 milliliters of glacial aceticacid to convert the lithium mercaptide to mercaptan. The total mixturewas then washed five times with 40-milliliter portions of boiled waterafter which the solvent was stripped under reduced pressure. Strippingwas continued until the product reached constant weight. It was storedunder nitrogen. The product was a colorless liquid Which had thefollowing properties:

Inherent viscosity 1 0.16 Gel, wt. percent 2 0 Refractive index, 11 31.5158

One-tenth gram of polymer was placed in a. wire cage made from -1neshscreen and the cage was placed in ml. of toluene contained in awide-mouth, 4ounce bottle. After standing at room temperature(approximately 25 C.) for 24 hours, the cage was removed and thesolution was filtered through a sulfur absorption tube of grade Cporosity to remove any solid particles present. The resulting solutionwas run through a Medalia-type viscometer supported in a. 25 C. bath.The viscometer was previously calibrated with toluene. The relativeviscosity is the ratio of the viscosity of the polymer solution to thatof toluene. The inherent viscosrtyns calculated by dividing the naturallogarithm of the relative viscosity by the weight of the originalsample.

De term1nati0n of gel was made along with the inherent viscositydetermination. The wire cage was calibrated for toluene retention inorder to correct the weight of swelled gel and to determine accuratelythe weight of dry gel. The empty cage was immersed in toluene and thenallowed to drain three minutes in a closed wide-mouth, two-ounce bottle. A piece of folded quarter-inch hardware cloth in the bottom of thebottle supported the cage with minimum contact. The bottle containingthe cage was weighed to the nearest 0.02 gram during a minimum threeminute draining period after which the cage was withdrawn and the bottleagain weighed to the nearest 0.02 gram. The difference in the twoweighings is the weight of the cage plus the toluene retained by it, andby subtracting the weight of the empty cage from this value, the weightof toluene retention is found, i.e., the cage calibration. 1n the geldetermination, after the cage containing the sample had stood for 24hours in toluene. the cage was withdrawn from the bottle with vthe aidof forceps and placed in the two-ounce bottle. The same procedure wasfollowed for determining the weight of swelled gel as was used forcalibration of the cage. The weight of swelled gel was corrected bysubtracting the cage calibration.

The cage, after removal from the twoounce bottle, was placed in analuminum weighing dish of known weight and the cage and dish were placedin a vacuum drying oven at 7080 C. for one hour after which they wereallowed to cool to room temperature and weighed. Subtracting the sum ofthe weights of the aluminum dish and the cage from the latter weighinggave the weight of the gel which was finally corrected for solutionretention on the cage and for soluble polymer remaining within the gelstructure.

The sample was placed on the prism of a Model 808 Spencer Lens Companyrefractometer, The refractive index was determined at 25 C.

The sample (0.1250 gram) was burned in an atmosphere of purified air at1000 C. and the gases were passed into a 3 weight percent neutralizedH202 solution. After the organic matter was burned, pure oxygen waspassed through the system for five minutes to insure completecombustion. The solution in which the burned gases were absorbed wastitrated as H2804 with 0.0550 N NaOH using methyl purple indicator.

A solution of 0.5410 gram polymer in 50 m1. toluene was prepared and 3.0ml. of this solution was added to 100 ml. of a 20 volume percentsolution of methanol in toluene. One ml. of 30 weight percent ammoniumnitrate in concentrated ammonium hydroxide was added and the mixture wastitrated amperometrically with a rotating platinum electrode against aHgHgIz electrode, the diffusion current being measured. A 0. 0040 Nsolution of silver nitrate in isopropanol was used in the titration,2.46 ml. being required. The end point was determined graphically.

The above data show that my inventioncan be practiced using a monolithicinitiator and the terminally reactive polymer formed can be modifiedwith a cyclic disulfide to produce a polymer containing mercapto groups.This liquid polymer can be cured by heating to substantially increaseits inherent viscosity.

Example 11 1,2-dilithio-1,2-diphenylethane was prepared in accordancewith the following recipe:

Grams Trans-1,2-diphenylethylene 18 (0.1 mole). Diethyl ether (220 ml.)1 157. Tetrahydrofuran (20 ml.) 2 17.8 (0.24 mole). Lithium wire 1.9(0.27 gram atom).

1 Dried over sodium. Distilled from lithium aluminum hydride and storedover sodium wire.

lowing recipes:

Parts by Weight Butadiene 100 100 Cyolnhe "me 780 Toluene 870l,2-Dilithio-1,Z-diphenylethane 1 3.88 1 3.88 Temperature, C 50 50 Time,hours 0.7 0. 7 Conversion, percent 100 100 1 (20 moles.)

After the polymerization was complete each reaction mixture was cooled,with agitation, to 5 C. and 40 millimoles of 1,2-dithiane as a 0.5 molarsolution in toluene was added slowly with agitation. During the reactionwith 1,2-dithiane, the temperature was controlled with a 5 C. bath.Clear, water white clumps of material formed upon the addition of1,2-dithiane, and as the reactions approached completion, the mixturesset up. Four hours was allowed for each reaction. Two control runs weremade in accordance with recipes A and B using the same procedure exceptthat no 1,2-dithia-ne was added.

Ten milliliters of glacial acetic acid was added to each reactionmixture while the temperature was maintained at 5 C. The mixture whichhad set up became fluidized upon addition of the acid. This treatmentconvented the lithium mercaptide end groups to mercapto (SH) groups andlithium acetate precipitated. Samples were withdrawn and titratedarnperometrically with silver nitrate. Results gave the following valuesfor milliequivalents of mercaptan per 100 grams of monomer charged:

Recipe A 35.6 Recipe B 34.6

The product from each run was isolated by precipitation in isopropanolwith one part by weight 'of antioxidant AO-2246 [2,2methylene-bis(4-methyl-6-tert-butylphe- 1101)] added per 100 parts byweight of monomer charged. The isopropanol was decanted and each productwas dried under reduced pressure in a nitrogen atmosphere. The

materials were colorless liquids which had properties:

the following Recipe A Recipe B Oon- 1,2-Di- Oon- 1,2'Ditrol thiane trolthiane Inherent Viscosity 1 0. 23 O. 81 0.23 0.50

Gel, wt. percent 1 0 0 0 0 Refractive index, m 3 1. 5112 1. 5173 1.5112 1. 5159 Sulfur, wt. percent 4 1. 71 1. 65 Sulfur,milliequivalents/lOO grams polymer 53. 4 51. 6 Mcrcaptan sulfur,milliequivalents/ 100 grams polymer 6 7. 30 7. 55

3 Same as in Example I.

4 The same procedure was used as in Example I with sample weights asfollows: A, 0.4433 gram; B, 0.4910 gram. In each case, after thetitration was run, barium chloride was added to precipitate the sulfuras B2180 The BaSO was then determined gravimetrieally. N 0 difference intotal sulfur was found using the two methods.

5 The procedure of Example I was followed. Details are as follows:

Grams polymer in 50 n11. toluene 0. 943 1. 006 Milliliters polymersolution used 5.0 5.0 Milliliters 0.0040 N AgNO; used intitration"..- 1. 72 1.

Example III LZ-dilithio-l,Z-diphenylethane was prepared as described inExample II and used as an initiator for the polymerization of butadiene.Polymerization recipes were as follows:

Parts by Weight Recipe A Recipe 13 Recipe 0 Butadiene 100 100Cyclohexane 780 780 780 l,2,-Dilithio-1,Z-diphenylethan l 1. 94 1 0.97 30. 39

1 10 millimoles. 2 5 millimoles. 3 2 millimoles.

Polymerizations were run at 50 C. and were continued to quantitativeconversion. The procedure following polymerization was the same as inExample 111 except that the amount of 1,2-dithiane added was 20, 10 and4 millimoles, respectively, in runs A, B, and C. A control run in whichno 1,2-dithiane was added was made in accordance with each recipe. M

After treatment with glacial acetic acid and isopropanol followed byisolation of the polymers, inherent viscosity and gel data wereobtained. The meroaptan content (milliequivalents/ 100 grams polymer)was determined on the dithiane-treated products. All products were thenheated at 307 F. and inherent viscosity and gel were deacaaeca lltermined. Swelling index values were obtained on the dithiane-treatedmaterials. Results were as follows:

12 order, by syringe. The bottles were then pressured to 25, psi. withnitrogen.

Runs

A B O 1 (Con- 2 1 (Con- 2 1 (Con- 2 trol) trol) trol) Original Polymers:

, Inherent viscosity 1 0.32 1. 68 0. 66 3. 07 1. 20 3. 59 Gel, wt.percent 1 0 0 0 0 0 Sulfur, wt. percent 4 0 58 0.26 0.10 Sulfur,milliequivalents/IOO g.

polymer. 18.1 8.1 3.1 Mercaptan sulfur, milliequivalents/ 100 g. polymer5 2. 90 0. 82 0. 67 Heated at 307 F., hours 2. 2 1.1 2. 2 1.1 2. 2 1.1

inherent viscosity 0.37 1. 81 0. 61 3. 76 1. 18 gel, wt. percent 2 0 520 24 0 7O swelling index 61 103 45 Not determined on sample with such ahigh gel content. 2 Same as in Example I. 4 The samples were burned at2500-3000 F. in an atmosphere of pure oxygen. The

gases were passed through a weight percent H01 solution. Titration wasmade continuously as gases were passed through the HCl solution usingstandard K10 solution (0.1 mg. sulfur per ml.) and starch as theindicator. Weight of samples burned: A-2, 0.0986 g.:

B-2, 0.0578 g. 0-2, 0.1223 g.

B The procedure of Example I was followed. Details are as follows:

B This determination was made along with the gel determination. Swellingindex is calculated by dividing the weight of swelled gel by the weightof dry gel.

The original control polymers from runs A and B were viscous liquidswhile that from run C was a soft solid. No significant change occurredafter heating these materials. The product from run A-2 was a verysticky solid which exhibited cold flow, that from run B-2 was a stickysolid which exhibited some cold flow but much less than in run A2, andthat from run C-2 was a slightly sticky solid. These1,2-dithiane-treated polymers, when heated, cured to clear or slightlyopaque solids. Oured products from runs A-2 and B2 exhibited slightstickiness while that from run C-2 was not sticky. These datademonstrate that the dithiane-treated products are self-curing.

Example IV iButadiene was polymerized in accordance with the followingrecipe:

Butadiene, grams 100 Toluene, grams i 5801,2-dilithio-1,2-diphenylethane, millimoles 1 Temperature, O 50 Time,hour 0.6 Conversion, percent 100 1 Prepared at about C. and allowed tostand overnight. Recipe as follows:

1,2-di hen leth lene trans-stiL bon g iwj 1 8.0 (0.1 mole).'letrahydrofuran, sml 20 (0.24 mole). Diethyl ether, ml 220.

Lithium wire, g 1.7 (0.24 g. atom).

After polymerization was complete, a solution of 1,2- dithiane intoluene was added by syringe using 4.8 grams (40 millimoles) per gramshutadiene. 'I he dithiane was added in small portions with frequentshaking to facilitate the reaction, five hours being required foraddition of the requisite amount to each bottle. The bottles wereallowed to stand overnight and 10 ml. of glacial acetic acid was addedto each by syringe. The mixtures fluidized immediately upon addition ofthe acid. The bottles were uncapped and contents poured into 2.5 litersof lSOPlO? panol containing 200 of Water and 1.5 grams of theantioxidant, 2,2-methylenebis(4-methyl 6 tert-butylphenol). In this stepthe materials from the three runs were combined and coagulated. Theisopropanol was decanted, the polymer was washed with 100 ml. ofisopropanol, and more of the antioxidant was mixed into the polymer byhand, one gram per 100 grams monomer charged being used. The polymer wasdried under nitro-' gen in a vacuum oven at room temperature. It had aninherent viscosity of 0.35 and was gel free.

'I'wo samples of polybutadiene were prepared and isolated in a mannersimilar to that described above except that they were not treated with1,2-dithiane. One sample was prepared using a 20 millimole initiatorlevel as given in the foregoing recipe. In the other run, 5 millimolesof initiator was used. The products were gel free and had inherentviscosities of 0.25 and 0.59, respectively.

Curing studies were carried out on the dithiane-treated polymer and oneach of the polybutadiene samples. Dicumyl peroxide was used in someruns and a combination of dicumyl peroxide and Hi-Sil 233 in others.(HiSil 2.33 is a hydrated silica pigment of extremely fine particlesize.) All compositions were cured 30 mimnutes at 307 13 F. Gel,swelling index, and V values were determined. Results were as follows:

The superiority in properties of the dithiane-treated polymer is evidentfrom the foregoing data.

Hi-Sil Dicumyl Gel 1 Swell- No. Polymer 233 Peroxide Percent ing V, 1

phr. B phr. B Index 1 Dithiane-treated polybutadiene. 0. 04 e 31 41 2 dn0.06 I 65 22 0.1080

R .dn 50 0.08

9 tio 50 0.10

15.- Polybutadiene 0.5

16.. Polybutadiene 0. 08

7 The Vr determination was made by cutting samples of the cured polymerweighing approximately 1.5 grams from regular tensile slabs, weighingthem on an analyt cal balance and allowing them to swell in n-heptanefor six days at 30 C. The swollen specimens were blotted with filterpaper and transferred imbibed solvent was obtained by dividing sampleand the weight of the dry, density of the solvent.

quickly to tared weighing bottles. The volume of the difierence betweenthe weight of the swollen extracted sample (dried 16 hours at 70 C. invacuo) by the Next the dry samples were weighed in methanol and theirvolume calculated. From this volume was subtracted the volume of fillers(calculated from the recipe and original sample weight) giving thevolume of polymer.

calculate the volume fraction of polymer in the swollen stock (Vr).

described in Rubber World, 135, No. 1, 67-73 (1956).

These data show that curing occurred with dicumyl peroxide alone evenwhen used in small quantities. Increasing the amount of the peroxideincreased the cure level, as evidenced by gel, swelling index, and V,data. In runs 15 to 18, the polymers did not contain mercapto groups. Nocuring occurred in runs 15 and 16, evidenced by lack of gel. Some curingoccurred in runs 17 and 18 but not nearly so much as with equivalentquantities of the same compounding ingredients in mercapto-containingpolymers. A very satisfactory cure level was achieved in run 3 whereasno curing was obtained using the same amount of dicumyl peroxide inpolybutadiene (run 1 6). It is thus seen that dicumyl peroxide effectedcuring in addition to that effected by the reactive end groups in thepolymer. Gel and swelling index values were not obtained onsilica-reinforced stocks.

Sixty grams of the foregoing dithiane-treated polybutadiene wasdissolved in 150 ml. toluene, precipitated in one liter of isopropanolcontaining 0.3 gram of 2,2- methylene-bis(4-methyl 6 tert-butylphenol),decanted, and dried under nitrogen in a vacuum oven at room temperature.The purified product had an inherent viscosity of 0.41 and was gel free.

There was substantially no diiterence between this polymer and theoriginal dithiane-treated product. The reprecipitated material wascompounded using 0.10 phr. dicumyl peroxide and 50 phr. Hi-Sil 233. Asample of the polybutadiene used in runs 16-18 was compounded using 50phr. Hi-Sil 233 and 0.50 phr. dicumyl peroxide. Both stocks were cured30 minutes at 307 F. and physical properties determined. Results were asfollows:

The latter was used to This method is Having thus described theinvention by providing specific examples thereof it is to be understoodthat no undue limitations or restrictions are to be drawn by reasonthereof and that many variations and modifications are within the scopeof the invention.

1 claim:

1. A process for the preparation of a self-curing polymer whichcomprises reacting a terminally reactive polymer having the formula PTwherein P comprises a polymer of polymerizable vinylidene compounds,said polymer having carbon to carbon unsaturation in the main polymerchain, T is a terminally positioned alkali metal, and x is an integer of1 to 4, with a reactant material selected from the group consisting ofss R R R I I l H-(5-Y--]7-H S R R 1i. R wherein R is selected from thegroup consisting of hydrogen and alkyl radicals containing 1 to 3 carbonatoms, Y is a divalent organic radical containing from 1 to 12 chainmembers selected from the group consisting of alkylene radicals,.alkenylene radicals and radicals containing groups selected from thegroup consisting of R! O, 1 1', and S said groups being linked betweencarbon atoms, with each R being an alkyl radical containing 1 to 3carbon atoms, and replacing the alkali metals in the polymer productwith hydrogens.

The 300% modulus, tensile strentth and elongation of the polymer sampleswere determined by a modification of ASTM 13412-51T. Test specimens weredied out of slabs 20 mils thick using Type D die.

These specimens measured 4 long and 0.125 wide in the flat test section.Stress-strain properties were obtained at 73=b2 F. The cross-head speedin these tests was 20 per minute.

aoaasea copolymer of butadiene and styrene and the reactant 7 materialis 1,2-dithiacyclohexane.

5. The process of claim 1 in which the polymer is a polymer of isopreneand the reactant material was 1,2- dithiacyclohexane.

6. The process of claim 1 in which the polymer is a polymer of butadieneand the reactant material is 1,2- I

dithiacyclopentane.

7. The process of claim 1 in which the polymer is a polymer of butadieneand the reactant material is 1,2- dithiacycloheptane.

8. A polymer prepared in accordance with the process of claim 1.

9. A polymer prepared in accordance with the process of claim 2.

10. A process for the preparation of solid polymer which comprisesreacting terminally reactive polymer having the formula PT wherein Pcomprises a polymer of conjugated dienes, said polymer having carbon tocarbon unsaturation in the main polymer chain, terminally T is apositioned alkali metal, and x is an integer of 1 to 4, with a reactantmaterial selected from the group consisting of R R I $1 0, N, and S saidgroups being linked between carbon atoms, with each R being an alkylradical containing 1 to 3 carbon atoms, replacing the alkali metals inthe polymer product with hydrogens, and thereafter reacting molecules ofsaid 16 polymer by heating at a temperature inthe range of to 500 F. 7

11. The process of claim 10 in which the polymer is a polymer ofbutadiene and the reactant material is 1,2-dithiacyclohexane.

12. The process of claim 11 in which the reaction of the molecules ofsaid polymer is carriedout in the presence of a conventional curingsystem.

13. Polymer prepared according. to the process of claim 10. Y

14. Polymer prepared according to the process of claim 11.

15. Polymer prepared. according to the process of claim 12.

16. A process for the preparation of a self-curing polymer whichcomprises reacting homopolymer of butadiene containing terminal alkalimetal atoms with 1,2-dithiacyclohexane at a temperature in the range of10 to +100 C. and replacing the alkali metals in the polymer productwith hydrogens.

17. A process for the preparation of solid polymer which comprisesreacting homopolymer of butadiene containing 2 terminal lithium metalatoms per molecule with 1,2-dithiacyclohexane at a temperature in therange of -100 to +100 0., replacing the alkali metals in thepolymer'product with hydrogens and thereafter reacting molecules of thehydrolyzed product by heating at a temperature in the range of 100 to500 F.

18. The process of claim 17 in which heating of the molecules of polymerproduct is carried out in the presence of a conventional curing system.

19. Polymer prepared according to the process of claim 17.

20. The process of claim 18 in which the conventional curing systemcomprises dicumyl peroxide.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Barber et al.: J. Chem. Soc., 1928, pp. 1141-1149. Barltropet al.: J. Am. Chem. Soc., 76, 4348 (1954) Gaylord et al.: Linear andStereoregular Addition Polymers, pp. 236-237, Interscience PublishersInc., NY. (1959).

1. A PROCESS FOR THE PREPARATION OF A SELF-CURING POLYMER WHICHCOMPRISES REACTING A TERMINALLY REACTIVE POLYMER HAVING THE FORMULA PTXWHEREIN P COMPRISES A PLOYMER OF POLYMERIZABLE VINYLIDENE COMPOUNDS,SAID POLYMER HAVING CARBON TO CARBON UNSATURATION, IN THE MAIN POLYMERCHAIN, T IS A TERMINALLY POSITIONED ALKALI METAL, AND X IS AN INTEGER OF1 TO 4, WITH A REACTANT MATERIAL SELECTED FROM THE GROUP CONSISTING OFFIG-01 WHEREIN R IS SELECTED FROM THE GROUP CONSISTING OF HYDROGEN ANDALKYL RADICALS CONTAINING 1 TO 3 CARBON ATOMS, Y IS A DIVALENT ORGANICRADICAL CONTAINING FROM 1 TO 12 CHAIN MEMBERS SELECTED FROM THE GROUPCONSISTING OF ALKYLENE RADICALS, ALKENYLENE RADICALS AND RADICLSCONTAINING GROUPS SELECTED FROM THE GROUP CONSISTING OF